1. Field of the Invention
The present invention is directed to an apparatus for forming depressions in the surface of the road, and in particular, to a high speed grinder for forming a series of spaced apart depressions in the pavement.
2. Prior Art
Rumble strips or sonic noise alert pattern (SNAP) depressions in the surface of the road are well known. Such depressions generate an easily heard noise when a vehicle drives over such a stretch of pavement. In addition, vibration is usually passed to the driver and passengers of the vehicle, alerting them that they have passed over such a pattern of depressions. Such SNAP depressions are often placed at the side of the road on the shoulder to alert a driver that the vehicle has veered off the driving lane and onto the shoulder, as may happen when drivers fall asleep at the wheel. In addition, rumble strips are placed within the lanes of the road to alert the driver that he/she is approaching a stop and to slow down in anticipation of the upcoming stop.
It can be appreciated that forming such depressions in the road usually requires a grinding device that must rise and full in a predetermined cycle to create a series of substantially evenly spaced apart depressions. For very hard pavement surfaces, such as concrete surfaces, the power required is substantial in order to form the depressions. The speed of forming such depressions is generally quite slow, on the order of a few hundred yards per hour. When miles of such SNAP depressions must be placed on the shoulder, the work can be a very time consuming process. In addition to the time required, the costs become substantial for a crew and the grinding equipment. Besides the costs of forming the strips, the inconvenience to the drivers using the road, including lane closures, can be substantial, causing severe traffic delays.
Prior devices for forming such strips are shown in U.S. Pat. Nos. 5,607,225, 5,391,011 and 5,484,228, to Thomas et al. These patents show a device and method for making SNAP depressions in the surface of pavement. The devices generally mount to a small skid steer loader device that has relatively little power for such an operation. In addition, the devices utilize an attachment that includes a cam type member engaging the surface of the road. Spacing of depressions and raising and lowering of the cutting head are linked directly to the movement of the cammed follower. Although the Thomas devices may provide for cutting a series of SNAP depressions, the speed at which such a device may travel is very limited due to the inadequate power available to the cutting head. Moreover, problems are encountered when the follower slips or engages other irregularities in the road surface as it directly connects to and supports the cutting head, leading to an irregular pattern of depressions.
Another device for cutting depressions in the road is shown in U.S. Pat. No. 5,297,894, to Yenick. The Yenick patent shows a pivotally mounted cutting head with a pair of guide wheels and a cam at the rear of the cutting device to raise and lower the blades. The cam includes a chain arrangement with the guide wheels to raise and lower the cutting head to the proper depth. However, the pivoting arrangement does not provide sufficient power or speed for the cutting head. The Yenick device requires the blades to follow a cam member with a wheel engaging the outer periphery of the cam. Although this eliminates the problems of a cam directly engaging the road surface, it is possible for the chain of the Yenick device to slacken or for the follower wheel to disengage the cam member, thereby leading to irregularities in the depression pattern.
It can be seen then, that a new and improved method and apparatus for cutting evenly spaced apart depressions in the surface of pavement is needed. Such a device should provide for directly lowering and raising the cutting head without use of a pavement engaging cam member and a follower. Such a device should support the cutting head and carriage from above for lowering or raising without directly engaging irregularities in the road surface from a follower wheel supporting the carriage. Such a device should provide sufficient power and direct support for raising and lowering the cutting head in a predetermined pattern at sufficient speed to cut even hard pavement material at speeds of over one mile per hour. In addition, such a device should provide for varying the length and spacing of the cuts and for easily varying cut parameters during operation. The present invention addresses these as well as other problems associated with cutting a series of depressions in the surface of the pavement.
The present invention relates to an apparatus for forming rumble strips, also known as Sonic Noise Alert Pattern (SNAP) depressions in the surface of the road. The grinding apparatus includes a support frame that supports a grinding carriage on its own movable frame. The carriage can be moved between a raised travel position and a lowered cutting position.
The carriage includes drive wheels at the rear of the carriage and a center wheel before the carriage. The carriage is supported off of two parallel transversely extending rotating shafts. The shafts include a central large diameter portion and smaller diameter end portions. The axes of the large and small diameter portions are offset so that rotation of the shafts provides eccentric motion. Therefore, the carriage, supported on the central large diameter portion, moves up and down as the shafts are rotated in parallel. This provides for an even support between the front and rear of the carriage. The arbor rises and falls with the carriage and is positioned with one support shaft in front of the arbor and the other behind. The support shafts are driven directly off the drive wheels so that changes in speed of the apparatus are reflected in the up and down motion of the carriage, thereby maintaining an evenly spaced pattern of depressions. However, the arbor is driven by a separate motor, so that cutting speed is not affected should there be increases or decreases in speed of the grinder.
The present invention also provides improved quality in the cutting pattern, as the arbor rotates with an upcut wherein the forward leading portion of the arbor relative to the grinder travel direction is rotating upward relative to the surface of the ground while the back of the cutting teeth are rotating downward into the ground. This motion is opposite the direction of the rotating carriage support shafts. The support shafts rotate so that the carriage is moving rearward relative to the grinder during the cutting portion of their travel. As the teeth disengage the ground, the arbor begins moving forward relative to the grinder apparatus. Therefore, since the grinder is moving forward, but the carriage is moving rearward relative to the grinder, there is less forward movement of the arbor relative to the ground than movement of the grinder. This prevents the teeth from being dragged forward as fast as the rate of travel of the grinder apparatus and shortens the length of the cut. However, when the arbor is raised above the ground and the carriage is moving forward as is the grinder, the carriage and cutting teeth accelerate forward while raised to a spaced apart position from the prior cut. This provides an even spacing pattern between adjacent cuts at greater speed. In addition, the spacing remains constant even if changes in the speed of the drive wheels occur and eliminates extra follower wheels.
For improved cutting and balance, the carriage includes counterweights offset from the arbor drive motor at a diametrically opposed corner of the carriage. In addition, the rotating carriage support shafts include a stack of weights that are supported about the shafts opposite of the carriage so that the power needed to raise and lower the carriage is decreased and there is better balance about the rotating shafts. The apparatus also includes separate support wheels for transporting and steering the apparatus when not cutting. The carriage forward wheel and drive wheel are spaced closer together on the support frame than the forward steering wheel and transport drive wheels so that the arbor more closely follows the contour of the ground and does not overcut or undercut in peaks and valleys. The grinder also includes height adjustment for raising or lowering either side of the carriage during operation to vary cutting depth for irregularities encountered in the pavement surface.
These features of novelty and various other advantages which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to the accompanying descriptive matter, in which there is illustrated and described a preferred embodiment of the invention.